Pipe Pressure Drop Calculator
Calculate friction head loss (Hazen-Williams) for water systems, HVAC, and plumbing networks.
Estimated Friction Loss
What is Friction Head Loss?
When a fluid, such as water, travels through a pipe, it experiences resistance due to friction against the inner walls of the pipe and internal friction between the fluid particles themselves. This resistance causes a dissipation of energy, directly resulting in a pressure drop along the line.
In hydraulic engineering and HVAC systems, accurately calculating this loss is critical for correctly sizing a pump's Brake Horsepower (BHP). If the pump cannot overcome this friction, the water will not reach its destination with the required flow rate or pressure.
The Hazen-Williams Equation
While the Darcy-Weisbach equation is theoretically more rigorous, the empirical Hazen-Williams formula is the industry standard for water flow at ambient temperatures. It is widely preferred because it does not require calculating the Reynolds Number or iterative friction factors.
Where (in US Customary Units):
- hf = Friction head loss in feet of water per 100 feet of pipe
- Q = Volumetric flow rate (GPM)
- C = Hazen-Williams roughness coefficient (dimensionless)
- d = Inside diameter of the pipe (inches)
Note: This calculator uses the universal metric base equation internally and converts the results to your preferred units to guarantee absolute precision.
The C-Factor and Fluid Velocity
The C-Factor determines how "smooth" the inside of the pipe is. Plastic materials like PVC (C=150) or Polyethylene offer much less resistance than an aged steel or cast iron pipe (C=100).
Additionally, this calculator verifies the fluid velocity (V = Q / A). In standard industrial and plumbing installations, it is highly recommended to keep water velocity between 3.5 ft/s and 8 ft/s. Velocities exceeding these limits dramatically increase pressure drop, system noise, and the risk of a destructive "Water Hammer" effect when valves are closed quickly.